The present invention relates generally to integrated circuits (ICs). More specifically, the invention relates to IC packages with additional contact points without increasing the size of the IC package.
Integrated circuits are used in almost all digital systems. Different types of integrated circuits with different types of packages cater to the needs of various applications. As portable applications like digital cameras and mobile phones require extremely small form-factors, the size of the device used in many of these applications should be minimized. Normally, the size of the device used is determined by the I/O requirement of the application that the device is used for. For example, an application that needs to have a certain number of I/Os will need to use a device that can meet that requirement. As these devices need to go through a series of tests, there needs to be resources on the device for testing. Therefore, the package of the device needs to have a sufficient number of leads to accommodate a variety of requirements.
The I/O requirement for a design is usually more than what is needed to test the device. A bigger package is generally needed when more I/Os are needed in a design. However, there are also cases where the total I/O requirement is less than what is needed to fully test the device. Therefore, the smallest device/package combination is determined by the minimum amount of test pins required to test the device in the package. Test requirements or test I/Os needed to test an IC device in a package is generally limited to the number of leads on the package. For example, a design might need only 16 I/Os but the minimum test requirement for the device used might be more than 16 I/Os. Hence, the minimum package size will be determined by the test requirement in this case because more leads are needed for testing than for I/Os. In other words, the lead count on a package must fulfill not only the I/O requirement of a design, but also the number of test pins needed to test the device in the package.
If the test program needed for testing an IC or a design requires more I/Os than available on a given package, then the device/package combination cannot be made. The size of a device, and subsequently the size of the package of the device, is therefore generally determined by the I/O requirement of a design. In cases where the total number of I/Os required in a design is less than the number of test pins needed to test the device used, the size of the package is still determined by the number of test pins needed and not the actual I/O requirement. It is not possible to use a smaller package even though the number of I/Os needed is significantly less.
However, because the size of the device and subsequently, the size of the package matters in some cases, the ability to have a device/package combination with less I/O count than is required for testing is desired. It is also advantageous to have a smaller package size which is not limited by the number of leads needed for testing the device in the package. It is further desirable to have leads of different elevations and to have the ability to test a device in a package at different elevations so that custom packages with the minimum required lead count can be used without affecting the test requirements for the IC device.